The circuit is composed of amplifier, comparator and an output control part. According to Faraday's law, person's body temperature is about 37 ℃, radiation infrared wavelength is about 10μm, the pyroelectric sensor selects P7178 with 7 ~ 20μm sensitive wavelength range. A1 and A2 are selected low noise, low loss CMOS op amp μPC358, and it is connected to band-pass filter composed of RC to prevent the entry of the noise and error signal, extracting only a signal when the human body moves. A3 and A4 constitute a comparator.
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Often, people attempt to control DC motors with a variable resistor or variable resistor connected to a transistor. While the latter approach works well, it generates heat and hence wastes power. This simple pulse width modulation DC motor control eliminates these problems. It controls the motor speed by driving the motor with short pulses. These pulses vary in duration to change the speed of the motor. The longer the pulses, the faster the motor turns, and vice versa. (View)

In the circuit, when E, O are input DC voltage, the motor will be moved to a position corresponding with the voltage. The potentiometer connected to the same coaxially of motor is used as position feedback. When the given voltage is equal to 1k potentiometer wiper contact voltage, the differential amplifier output is zero, so the motor is stationary; Otherwise, the motor will be transferred or reversal according to the size of the signal.
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